Thanks for your answer.
Are you on a 64 bit ubuntu?
No !
I have put "libjinput-linux.so" at the root of my project, and found a solution with a VM argument :
-Djava.library.path="./"
It works fine

But the keyboard is not found

just my gamepad. I have the message :
Loading: net.java.games.input.LinuxEnvironmentPlugin
Failed to open device (/dev/input/event3): Failed to open device /dev/input/event3 (13)
Failed to open device (/dev/input/event6): Failed to open device /dev/input/event6 (13)
Failed to open device (/dev/input/event5): Failed to open device /dev/input/event5 (13)
Failed to open device (/dev/input/event4): Failed to open device /dev/input/event4 (13)
Failed to open device (/dev/input/event2): Failed to open device /dev/input/event2 (13)
Failed to open device (/dev/input/event1): Failed to open device /dev/input/event1 (13)
Failed to open device (/dev/input/event0): Failed to open device /dev/input/event0 (13)
Linux plugin claims to have found 1 controllers
-> Stick
Saitek P990 Dual Analog Pad
And the buttons and paddle are without effects !

(with ubuntu, not with Windows)
I am going to try the latest nightly...